Anomalous slow-down of the bound state dynamics in a non-locally coupled quantum circuit

TL;DR

This paper demonstrates that in a non-locally coupled quantum circuit, the dynamics of a bound state can become unexpectedly slow at specific NNN hopping strengths, due to destructive interference effects, as shown through simulations and numerical analysis.

Contribution

It reveals a novel slow-down phenomenon in bound state dynamics caused by non-local couplings, supported by quantum simulations and theoretical analysis.

Findings

Slowing down occurs at a specific NNN hopping strength.

Bound state band exhibits a quasi-flatband feature.

Destructive interference causes the anomalous slowdown.

Abstract

Additional hopping channels in a tight-binding lattice is known to introduce faster dynamics of a quantum mechanical particle. However, we show that in the case of a repulsively bound state, the dynamics becomes abnormally slow when next-nearest neighbor (NNN) hopping is allowed for the particles. We show that such slowing down occurs for some magic strength of the NNN hopping at which the bound state band exhibits a quasi-flatband feature. We reveal this anomalous dynamical behavior by analyzing the quench dynamics of two nearest neighbor (NN) spin excitations (magnons) on a ferromagnetic chain by allowing both NN and NNN couplings. By implementing digital quantum computing simulations on a NISQ device, we obtain such non-trivial signatures and complement the results with exact numerical calculations. Moreover, through perturbative arguments, we reveal that the slowing down is due to the destructive interference between different paths associated to the bound state dynamics.